It is known in the art that the salts of metals belonging to the group of lanthanides, together with alkyls of metals belonging to the main groups from 1 to 3 of the periodic table and in the presence of halogenating agents, can form active catalytic systems in the Ziegler-Natta type polymerization reaction of both olefinic and diolefinic unsaturated monomers.
The systems are among the most stereospecific and active for the 1,4-cis polymerization of butadiene and in addition the elastomer produced has better mechanical properties than those of the polybutadienes produced with other catalytic systems.
A vast collection of examples of ternary catalytic systems based on metal salts of the group of lanthanides is provided in the publication by G. Allen and J. Bevington "Comprehensive Polymer Science" Vol. 4, chapter 5 page 53, published by Pergamon Press in 1989.
Other particularly detailed references can be found in the articles appearing in the magazines Inorganica Chimica Acta, vol. 130 page 125 of 1987 and Polymer, vol. 29, page 1516 of 1988.
A metal belonging to the group of lanthanides refers, as is generally accepted in the known art, to a metal belonging to the group comprising: scandium, with atomic number 21, yttrium, having atomic number 39, and/or a metal having an atomic number between that of lanthanum (57) and that of lutetium (71); these metals belong to group IIIA of the periodic table, according to the IUPAC definition prior to 1985.
From the point of view of patents, valid examples of ternary catalytic systems based on lanthanides are represented by German patents DE 1.812.935, DE 2.833.721, DE 2.848.964 and DD 243.034.
In most of the above cases, the catalytic systems are prepared by mixing the three components directly in the presence of the unsaturated compound to be polymerized, a method known in the art as "in situ preparation of the catalytic mixture".
Another technique of the known art involves the preparation of the catalytic mixture in a suitable solvent (preformation) and then the resulting solution or suspension is put in contact with the solution of the unsaturated compound to be polymerized. In this latter case, the preformed mixture of the catalyst can be left to age for a fixed period before being put in contact with the unsaturated monomer to be polymerized.
In all of the above cases, the claimed mixtures form catalytic systems suitable for the polymerization of unsaturated monomers in general and in particular butadiene.
These catalytic mixtures, however, owing to their complexity, are not structurally defined and cannot be isolated as defined products, but must be used as such after the mixing of the components; it is not even possible to isolate the organometallic derivatives of the metals involved in the catalytic reaction.
On the other hand, apart from the advantage of having stoichiometrically well-defined products, especially when they are used as components of polymerization catalytic systems, it would also be useful for the reproducibility of the chemical-physical characteristics of the polymers produced. In other words, with catalysts deriving from well-defined products, polymers can be obtained having reproducible and constant molecular weights and molecular weight distribution.
Another advantage is that variations in the characteristics of the polymers can be programmed by varying the parameters relating to the catalytic component itself.